Substrate resistivity influence on silicon-germanium phototransistor performance

This Letter presents the impact of silicon substrate resistivity on SiGe phototransistors. SiGe phototransistors were fabricated on the commercially available SiGe/Si bipolar technology. The performances of the phototransistors fabricated based on low- and the high-resistive silicon substrate are compared. The phototransistor based on low-resistivity (LR) silicon substrate provides a responsivity of more than double compared to the phototransistor based on a high-resistivity silicon substrate that is fabricated by using the same bipolar transistor technology. The phototransistor fabricated on LR substrate exhibits low-frequency responsivity up to 1.35 A/ W (at 50 MHz).